Polyurethane oil de-emulsification unit

ABSTRACT

A process for separating an aqueous emulsion including an aqueous phase and an non-aqueous phase into separated aqueous and non-aqueous phases, to provide a recovered non-aqueous phase, and to provide a recovered aqueous phase containing an acceptable level of the non-aqueous phase. In the process, at least one body, and preferably two or more bodies, of polymeric material with a high surface area, typically a foam material or polymer chips, is used in a horizontal flow treatment system to break the emulsion and thus provide both the aqueous and non-aqueous phases as two separate flows. A wide range of polymers can be used in the system as the polymeric material including polyurethane, polypropylene, polystyrene, polyester, and polyethylene. If a very low level of non-aqueous phase in the effluent is required, for example to meet potable water standards, then a Kozlowski polyurethane, as described in U.S. Pat. No. 5,239,040, is preferred as the last polymeric material body.

In the recent past, there have been several well documented instances ofthe inadvertent spillage of liquids causing both environmental,ecological, and even toxicological problems for plant species, insects,wild life, and even people. Examples of spilled liquids include oils andsolvents, and a group of materials known loosely as PCB's. For many ofthese liquids, methods of clean up are known, even for relativelydifficult ones, such as crude oil and PCB's.

For many of these materials, a feasible method of both clean up andrecovery is described by Kozlowski, in U.S. Pat. No. 5,239,040. Thismethod has been shown to be both practical, and effective, in thatrather than simply dispersing the spilled liquid with, for example, adetergent, the spilled liquid itself is recovered. It is then possibleto separate the recovered liquid from the recovery agent so that therecovered liquid can be safely dealt with in an appropriate fashion, andso that the recovery agent itself an be re-used to capture more liquid.As described by Kozlowski, the recovery agent and the recovered liquidare separated by centrifugation. The recovery agent described Kozlowskiis a polyurethane foam material, which is prepared from specifiedreactants using a particular process. Hereafter this material will bedescribed as “Kozlowski polyurethane foam”.

In addition to its ability to function as a re-useable liquid recoveryagent, Kozlowski polyurethane has been shown to be useable to recover,for example, oil which has been spilled onto water. The Kozlowskipolyurethane has been shown to be able to absorb, for example, oil notonly when the foam is essentially dry but also when the foam isessentially fully wet or even waterlogged.

Another difficulty with spilt non-aqueous liquids arises when water ispresent. A water immiscible liquid can be present in association withwater in two quite different forms. At least a part of it will generallybe present as a discrete second phase, which may be heavier or lighterthan water. The remainder will generally be present as an emulsion, ofat least some level of stability, and in which water can be either thecontinuous phase or the disperse phase. In both cases, there is also thedifficulty that nearly all substances that appear to be immiscible withwater, for example light hydrocarbons such as benzene, in fact aresoluble in water to a small extent, often at a level of parts permillion. For an aqueous emulsion in which water is the continuous phase,Kozlowski, in WO 94/21347, disclosed that in addition to absorbing oildroplets dispersed as a second phase in water, Kozlowski polyurethane,even when water logged, will also absorb dissolved oil down to the lowlevels required for potable water.

In WO 94/21347 Kozlowski describes a water treatment procedure in whichthe tainted water is allowed to flow downwardly through successivelayers of Kozlowski polyurethane. The outflow of water has to bemonitored, and the foam layers removed to recover absorbed oil from themwhen the oil level in the outflow water rises to an unacceptable value.

Although the procedure described by Kozlowski in WO 94/21347 appears todeal with aqueous emulsions, in practise it has several disadvantages,the most relevant one being that all of the oil, both as disperse phaseand as solute, has to be absorbed by the Kozlowski polyurethane,recovered from it typically by centrifugation, and the Kozlowskipolyurethane re-used to recover more oil. It is thus apparent thattreating a large volume of water containing only relatively smallamounts of emulsified oil can become very time consuming. There istherefore a need for an alternative technique to the use of Kozlowskipolyurethane, as described in WO 94/21347, at least as a primarytreatment for dealing with aqueous emulsions.

The only other apparently viable alternative for dealing with emulsionsis to flocculate the droplets until a size is reached at whichseparation into two phases will occur. This will generally requireflocculation to a droplet size in excess of at least 30 μm. However,this technique requires the consumption of chemicals and the creation ofa chemical sludge. It is consequently not environmentally friendly inuse.

This invention seeks to overcome these difficulties, and to provide atreatment apparatus and process which will deal with aqueous emulsionsreasonably quickly, and which will provide the non-aqueous phase in arecoverable form.

This invention is based on the discovery that not only Kozlowskipolyurethane foam, but also other polymeric materials when fabricatedinto a body of high surface area material such as a foam, if used underthe correct conditions, will function as an emulsion breaker, and willseparate a flow of an aqueous emulsion into two separate phases. Suchconditions include adjusting the flow rate of incoming aqueous emulsionso that there is an adequate contact time between the aqueous emulsionand the polymeric material to effect separation of the non-aqueousphase, and to form a free floating non-aqueous phase layer. It has beenfound that when several polymeric materials when fabricated into a bodyof high surface area material are exposed, for example, to a flow of anemulsion of oil and water containing up to at least about 10,000 ppmdispersed oil, two processes appear to take place. First, the polymericmaterial absorbs oil before and until it becomes saturated with oil.Second, as the polymeric material continues to absorb more oil, itreleases as much oil as it absorbs, but it does so at a droplet sizewhich is sufficiently large to coalesce into a separate oil phase. It isthen possible to separate the aqueous and non-aqueous phases, andrecover each of the two phases separately. Further, by the use of aplurality of treatment steps, the majority of the emulsified non-aqueousmaterial can be recovered on a continuous basis, so that a Kozlowskipolyurethane foam absorbent only may be necessary for the last, or forthe last few, treatment steps in the sequence. The only significantrestrictions on the polymer material appear to be first the ability toform a high surface area material, such as a foam, from it, and secondthat the polymeric material chosen is resistant to degradation under theconditions of use; for example, a polyester material is not suitableunder alkaline conditions which will result in hydrolytic degradation ofthe polymer, but which would be resisted by a polyalkylene such aspolyethylene.

Thus in its broadest embodiment, this invention seeks to provide aprocess for separating an aqueous emulsion having a continuous aqueousphase and an non-aqueous disperse phase into separated aqueous andnon-aqueous phases, to provide a recovered non-aqueous phase, and toprovide a recovered aqueous phase containing an acceptable level of thenon-aqueous phase, which process comprises:

-   -   (a) contacting the flow of an aqueous emulsion with a first body        of polymeric material having a high surface area;    -   (b) continuing the flow of aqueous emulsion until a separate        non-aqueous phase is formed;    -   (c) adjusting the flow rate of the aqueous emulsion so that        there is an adequate contact time between the aqueous emulsion        and the polymeric material effecting a continuous separation of        the non-aqueous phase and to form a free floating non-aqueous        phase layer;    -   (d) separating the separated non-aqueous phase obtained in        steps (b) and (c) without stopping the flow of aqueous emulsion;    -   (e) recovering the separated non-aqueous phase obtained in        step (d) without stopping the flow of aqueous emulsion;    -   (f) recovering a flow of treated aqueous phase without stopping        the flow of aqueous emulsion; and    -   (g) repeating steps (a) to (f) to contact the flow of treated        aqueous phase with at least a second body of polymeric material        having a high surface area until the maximum acceptable level of        non-aqueous phase is reached in the flow of recovered aqueous        phase.

Preferably, the polymer used in the polymeric material is chosen fromthe group consisting of polyurethane, polypropylene, polystyrene,polyester, and polyethylene. More preferably, the polymeric material ispolyurethane.

Preferably, the polymer material having a high surface area is apolymeric foam material. More preferably, the polymer material having ahigh surface area is a particulate polymeric foam material.Alternatively, the polymer material having a high surface area is in theform of polymer chips.

Preferably, the flow of aqueous emulsion in step (a) contacts the firstbody of polymeric material in a flow direction chosen from the groupconsisting of horizontal, vertical downwardly, and vertical upwardly.

Preferably, a plurality of bodies polymeric material is used, the flowcontacts each of them in sequence, and separated non-aqueous phase isrecovered from the flow after the each body of polymeric material.Alternatively, a plurality of bodies polymeric material is used, theflow contacts each of them in sequence, and separated non-aqueous phaseis recovered from the flow after the each body of polymeric materialexcept for the last, and separated non-aqueous phase is recovered fromthe last body.

Preferably, when a sequence of bodies of polymeric materials is used, atleast the last body of polymeric material comprises a Kozlowskipolyurethane foam.

Preferably, the process further includes pretreatment steps prior tostep (a) in which steps:

-   -   (h) non-aqueous phase droplets large enough to coalesce are        allowed to form a separated non-aqueous phase,    -   (i) the separated non-aqueous phase is recovered, and    -   (j) the aqueous phase is recovered and used as the flow in step        (a).

The invention will now be described by way of reference to the attacheddrawings in which:

FIG. 1 shows schematically a three unit treatment system;

FIG. 2 shows schematically an alternative unit;

FIG. 3 shows graphically the performance of Kozlowski polyurethane andfour other commercially available polyurethane materials;

FIGS. 4, 5, 6 and 7 show graphically the performance of foams ofpolyurethane, polypropylene, polystyrene, polyester, and polyethylene.

Referring first to FIG. 1, this shows schematically a three compartmentunit together with a pre-treatment unit. The treatment system 1comprises a set of boxes 2, 3, 4, 5, 6, 7 and 8. These can be fabricatedas separate units, or they can be fabricated in pairs as shown, or as asingle complete treatment system. A flow of incoming aqueous emulsion 9enters box 2, which is a pretreatment unit. The emulsion flow 9 willenter this box typically at about one third to one half way up from thebottom. In this box, any large droplets coalesce into a separatednon-aqueous phase 10, which is removed through the pipe 11.

The next box 3 has foraminous sidewalls 12 and 13, and a solid top sheet14. The box is packed with high surface area polymeric material 15,which is typically a foam. The foam is normally used in a particulateform, in part to assist in packing the box, and in part to ensure theexposure of a high surface area to the flow through the box. A typicalparticle size is from about 5 mm to about 20 mm. The separated aqueousemulsion phase 16 from box 2 enters box 3 through the wall 12, contactsthe polymeric material 15, and passes through wall 13 into box 4. In box3, further separation of the non-aqueous and aqueous phases occurs. Inbox 4, the two phases separate to provide a second separated non-aqueousphase 17 which is recovered through the pipe 18, and a treated aqueousphase 19 passes to box 5. As shown, box 4 includes an enlarged optionalcatchment space extending over the top of box 3.

Boxes 5 and 6 are constructed in the same way as boxes 3 and 4. Treatedaqueous phase 19 enters box 5 through the foraminous wall 20, contactsthe polymeric material 21, and leaves through foraminous wall 22. In box6 further non-aqueous phase 23 separates, is collected, and recoveredthrough the pipe 24. Twice treated aqueous phase 25 passes to boxes 7and 8, which again are the same as boxes 3 and 4, with a third body ofpolymeric material between two foraminous walls. In box 8 furthernon-aqueous phase 26 is collected and recovered through pipe 27, and aflow 28 of treated aqueous phase leaves the system from box 8. In eachof pipes 18, 24 and 27 a suitable flow control device is used, such as afloat operated automatic valve, or a time sequenced valve.

In the treatment system, the flow rate of incoming aqueous emulsion 9 isadjusted so that there is an adequate contact time between the aqueousemulsion and the polymeric material in boxes 3, 5 and 7 to effectseparation of the non-aqueous phase, and to form a free floatingnon-aqueous phase layer. In practise, this is generally found to besufficient to provide droplets having a size in excess of at least about150 μm.

If the acceptable level of non-aqueous phase in the treated aqueousphase 28 is extremely low, for example if the treated aqueous phase isintended to meet the standards for potable water, then it is recommendedthat at least the third body of polymeric material in box 7 should beKozlowski polyurethane foam. In that case, the Kozlowski polyurethanefoam will be acting as an absorbent only, and not as an emulsionbreaker. Consequently, when the third body—or the last if more thanthree are used—is a Kozlowski polyurethane foam functioning as only anabsorbent, a separate non-aqueous phase will not be formed, and therewill not be a non-aqueous phase flow in pipe 27. Instead, the treatedaqueous phase has to be monitored, so that when the Kozlowskipolyurethane foam becomes fully loaded with non-aqueous phase (whichwill be indicated by a rise in concentration in the treated flow 28) itis removed, and the non-aqueous phase recovered from it, typically bycentrifugation. In order to avoid having to cease processing whilenon-aqueous phase is recovered from the loaded Kozlowski polyurethane,it is convenient to provide two treatment units in parallel, which areused alternately.

Similarly, if the incoming aqueous flow 9 is heavily contaminated withthe non-aqueous phase, more than three polymeric material bodies may berequired. The number required will be largely determined by the level ofcontamination which is acceptable in the effluent water from thetreatment unit. If the incoming aqueous flow also contains solidmaterial, it is advantageous to provide a vent 29 from box 2 so thataccumulated solids can be periodically removed.

The polymeric material in the first compartment may also need to beinspected periodically, and replaced if it becomes clogged withsuspended small particle size solids in the aqueous flow which have notbeen separated in a pretreatment stage.

This unit has the advantage that the non-aqueous phase droplets as theyare detached from the body of polymeric material simply continue to riseaway from it, and it is only the treated flow which moves laterally.

In FIG. 1 the flow of aqueous emulsion through the bodied ofpolyurethane material in treatment stages is essentially horizontal. Itis also possible to arrange the treatment stages so that the flow passesthrough the polyurethane body essentially vertically, in either anupward or a downward direction. A suitable treatment unit is shown inFIG. 2 in which the flow passes in an upward direction.

In FIG. 2 the treatment unit 40 as shown is essentially a singlestructure: like the horizontal unit it can be made as one integralstructure or from several separate interconnected boxes. Aqueousemulsion enters the bottom of the unit through a pipe as at 41 into thefirst box 43. If desired, a drain 42 can be provided to deal with anysolids that accumulate in box 43. The boxes then alternate upwardly:boxes 43, 45, 47 and 49 contain the aqueous phase flowing through thetreatment unit, and boxes 44, 46 and 48 contain the high surface areapolymeric material. Catchment boxes 50, 51, 52 and 53 are then locatedbeside each pair of boxes. The construction and operation of boxes 43,44 and 50 is exemplary. The polymeric material is located on a grid 54,such as a perforated metal plate, and between the outer solid wall 56Aand inner wall 56B. The wall 56B includes a row of perforations or slotsacross the box 43 just below the grid 54. The top surface 57 of thecatchment box 50 is solid. As the emulsion encounters the saturated bodyof polymeric material body 58, the aqueous phase continues more or lessupwardly through it, and into the next box. If desired, a secondperforated metal plate 55 can be located above the body of polymericmaterial 56. As the polymeric material breaks the emulsion, theseparated oil droplets tend to collect on its lower surface, and tendnot to percolate through it; the separated oil droplets travel sidewaysthrough the perforations or slots in wall 56B into the catchment box 50.Separated oil collects as a second phase as at 59, and is removedthrough the pipe 60. Flow through the pipe 60 is again controlled in anysuitable way, for example a float controlled automatic valve or a timesequenced valve. The two following units operate in the same way, toprovide a treated water flow into the following box above, and an oilflow in the pipes 61 and 62.

How the last box 49, together with its catchment box 53, operate dependson the amount of oil still in the aqueous emulsion flow reaching it, andthe amount of oil that can be accepted in the effluent treated waterflow 64. In order to separate any free oil in the incoming water asuitable wire arrangement is provided between the box 49 and thecatchment box 53. If the last body of polymeric material in box 48 isKozlowski polyurethane foam that is functioning only as an absorbent,then there should be no separated oil flow into the catchment box 53,and hence no oil flow in the pipe 63. In the alternative, if the lastbody of polymeric material in box 48 is functioning to separate furtheroil, then it is possible that there can be some oil droplets in thewater in box 49. These are then trapped in the catchment box 53, andrecovered as an oil phase through pipe 63.

As described, the treatment unit in FIG. 2 includes three polyurethanebodies. How many bodies are used will be determined by essentially threefactors: the quantity of emulsion to be treated, the amount ofnon-aqueous material in the emulsion, and the quality level required inthe outflow of treated water. It is therefore possible the more than thethree units shown will be required in some cases. Since units of thistype are often required to be used either under adverse conditions, orunder conditions where only minimal supervision is possible, it ispreferred that the number of treatment units used should be more thananalyses indicate to be required, thus providing a safety margin.

In the practise of this invention, as noted above, if a very low levelof non-aqueous material in the aqueous phase is required it is usuallydesirable to use a Kozlowski polyurethane in at least the last treatmentstage. For the earlier stage, or stages, other polymeric materials canbe used. FIG. 3 shows comparative performance data for five differentpolyurethane materials. This data is based on a single pass test, inwhich an aqueous oil emulsion was passed through a body of each foammaterial, and the oil content at both inlet and outlet was determined.In these tests, a 10 cm diameter pipe was used containing fivecompartments. The second and fourth compartment, each about 4 cm inlength contained the test sample of polyurethane. The first, third andfifth compartment were empty, and about 0.8 cm in length. The flowthrough the test pipe was horizontal. The emulsion used was 10W30 motoroil mixed into water using a centrifugal pump at 3,450 rpm. The flowrate was constant, at 1.5 L/min.

In FIG. 3, the effluent oil level (vertical axis) is plotted against theinlet oil level (horizontal axis), in ppm on both axes.

The five polyurethane materials are identified as follows.

A: Kozlowski polyurethane foam.

B: Upholstery grade foam chips, composition unknown.

C: Great Stuff™ polyurethane foam.

D: Great Stuff™ expanding polyurethane foam.

E: All Direction Great Stuff™ polyurethane foam.

Product B is a standard commercial product available from many sources;its composition is not known. The product was supplied by Eversoft Fibreand Foam Ltd. Products C, D and E are all commercially available, andare made by Flexible Products Co., Joliet, Ill., USA. The maincomponents appear to be 4,4′-diphenylmethanediisocyante, apolyether/polyol blend, and a blowing agent. As FIG. 3 shows, all ofthese products are capable of significantly reducing the oil content ofthe oil and water system tested.

FIGS. 4, 5, 6 and 7 the results of similar test are shown using otherpolymeric materials, with a polyurethane foam included for comparison.In these tests, the cylinder contained four compartments packed with thepolymeric material, the flow rate was 1.2 liters/minute, and the testoil in the emulsion was 10W30 motor oil. The test polymers used were:

-   -   in FIG. 4, polyethylene;    -   in FIG. 5, polyester;    -   in FIG. 6, polystyrene; and    -   in FIG. 7, polypropylene.        The polyester and polyurethane were used as foams; the        polyethylene, polystyrene and polypropylene were used as high        surface area small particles, which were thin cutting        chips(similar to swarf) with a maximum dimension of about 5 mm.        In each experiment, the mixture of oil and water was passed        through the cylinder, and the oil level measured before and        after treatment. The oil level in the aqueous flow was not        constant.

In each of FIGS. 4-7 the horizontal axis is time in hours; and thevertical axes are in parts per million(ppm). The left axis refers to thetreated aqueous flow, and the right axis to the untreated aqueous flow;these axes are not to the same scale. In each Figure, trace A is theincoming aqueous oil containing flow; trace B is after treatment withpolyurethane, and trace C is after treatment with the test polymer. Ineach Figure the traces show that the amount of oil left in the aqueousflow is related to the amount of oil present initially. These tracesalso show that of the materials tested, the polyurethane appears to bethe most effective, and reduces the oil level to generally less than amaximum of about 50 ppm.

1. An apparatus for continuously separating a flow of an aqueousemulsion including an aqueous continuous phase and a non-aqueousdisperse phase to provide a flow comprising a non-aqueous phase and afurther flow comprising a recovered aqueous phase containing anacceptable level of non-aqueous phase, which apparatus comprises incombination at least a first compartment and a second compartmentwherein: (a) the first compartment includes a first feed means forreceiving the flow of aqueous emulsion into a first enclosure occupyingpart of the space within the first compartment, which first enclosure ispacked with a first body of high surface area particulate polymeric foammaterial, said first feed means comprising a fixed upstream foraminoussidewall of said first enclosure; an opposed fixed downstream foraminoussidewall forming part of the first enclosure through which a flowcomprising a non-aqueous phase component and an aqueous phase componentcan flow into a first separation space for phase separation of saidcomponents, said first separation space comprising the remainder of thespace within the first compartment; a first non-aqueous phase recoverymeans constructed and arranged to recover from the first separationspace a non-aqueous flow comprising said non-aqueous phase component;and a first aqueous phase recovery means constructed and arranged torecover from the first separation space a recovered aqueous flowcomprising said aqueous phase component; and (b) the second compartmentincludes a respective feed means for receiving said recovered aqueousflow into a respective enclosure occupying part of the space within thesecond compartment, which respective enclosure is packed with arespective body of high surface area particulate polymeric foammaterial, said respective feed means comprising a fixed upstreamforaminous sidewall of said respective enclosure; an opposed fixeddownstream foraminous sidewall forming part of the respective enclosurethrough which a flow comprising a respective non-aqueous phase componentand a respective aqueous phase component can flow into a respectiveseparation space for phase separation of said respective components,said respective separation space comprising the remainder of the spacewithin the second compartment; a respective non-aqueous phase recoverymeans constructed and arranged to recover from said respectiveseparation space a non-aqueous flow comprising said respectivenon-aqueous phase component; and a respective aqueous phase recoverymeans constructed and arranged to recover from said respectiveseparation space a recovered aqueous flow comprising said respectiveaqueous phase component.
 2. An apparatus according to claim 1 furtherincluding between the first and second compartments at least one othercompartment which together with the first and second compartmentsprovide a continuous flow path, wherein the at least one othercompartment includes: a further respective feed means for receiving therecovered aqueous flow from an immediately adjacent compartment upstreamin the flow path into a further respective enclosure occupying part ofthe space within said other compartment, which further respectiveenclosure is packed with a further respective body of high surface areaparticulate polymeric foam material, said further respective feed meanscomprising a fixed upstream foraminous sidewall of said furtherrespective enclosure; an opposed fixed downstream foraminous sidewallforming part of said further respective enclosure through which a flowcomprising a further respective non-aqueous phase component and afurther respective aqueous phase component can flow into a furtherrespective separation space for phase separation of said furtherrespective components, said further respective separation spacecomprising the remainder of the space within said other compartment; afurther respective non-aqueous phase recovery means constructed andarranged to recover from the said further respective separation space anon-aqueous flow comprising said further respective non-aqueous phasecomponent; and a further respective aqueous phase recovery meansconstructed and arranged to recover from said further respectiveseparation space a recovered aqueous flow comprising said furtherrespective aqueous phase component for delivery to an immediatelyadjacent compartment downstream in the flow path.
 3. An apparatusaccording to claim 2 wherein, for each compartment other than the firstcompartment, the feed means for receiving said recovered aqueous flowcomprises a common foraminous wall separating said compartment from theimmediately upstream compartment.
 4. An apparatus according to claim 1wherein for each enclosure the high surface area particulate polymericfoam material is the same.
 5. An apparatus according to claim 2 whereinfor each enclosure the high surface area particulate polymeric foammaterial is the same.
 6. An apparatus according to claim 1 wherein thehigh surface area particulate polymeric foam material for each enclosureis not the same.
 7. An apparatus according to claim 2 wherein the highsurface area particulate polymeric foam material for each enclosure isnot the same.
 8. An apparatus according to claim 1 wherein the highsurface area particulate polymeric foam material for each enclosurecomprises polyurethane.
 9. An apparatus according to claim 2 wherein thehigh surface area particulate polymeric foam material for each enclosurecomprises polyurethane.
 10. An apparatus according to claim 1 whichfurther includes a pretreatment unit having a feed means for receivingthe flow of aqueous emulsion, a pretreatment box and a recovery meansfor transferring a flow comprising an aqueous phase to the first feedmeans in the first compartment.